1. Technical Field of the Invention
The present invention relates in general to the mobile communications and Internet fields and, in particular, but not exclusively, to an Internet Protocol (IP)-based Base Station System (BSS) architecture for General Packet Radio Service/Enhanced Data Rates for Global Evolution (GPRS/EDGE) applications.
2. Description of the Prior Art
FIG. 1 is a block diagram of an existing BSS architecture for the GPRS. Referring to FIG. 1, the GPRS BSS includes a Radio Base Station (RBS) 10. The RBS includes a Channel Control Unit (CCU) 12. The RBS is connected to a Base Station Controller/Transcoder Controller (BSC/TRC) 14. The BSC includes a Packet Control Unit (PCU) 16. Notably, the PCU can also be located in the RBS 10. The BSC 14 is connected to a Serving GPRS Support Node (SGSN) 18. An Operations and Support System (OSS) 20 is connected to the BSC 14.
FIG. 2 is a block diagram of an IP-based BSS 200, which has been developed by Ericsson. A more detailed description of such an IP-based BSS is disclosed in the above-described commonly-assigned, co-pending U.S. Application for patent Ser. No. 09/494,606, the entire disclosure of which is incorporated herein by reference.
Referring to FIG. 2, the IP-based BSS 200 can include three types of nodes connected to an IP network 208. A mobile station 222 is connected to a Radio Base station 202, which is connected to the IP network 208. In general, the RBS 202 functions similarly to existing RBSs used for implementing a GSM model. Moreover, the RBS 202 also provides IP support for the BSS 200. For example, the RBS 202 functions as an IP host and can include an IP router (not shown). The IP router can be used to route payload User Datagram Protocol (UDP) datagrams to one or more Transmitter/Receivers (TRXs) and also for connecting a plurality of RBSs in various topologies.
A second node connected to the IP network 208 is a GateWay (GW) 204, which is then connected to MSC 218 and SGSN 220. The GW 204 can be used to terminate the A-interface. Also, the GW 204 can perform a conversion from one protocol (e.g., SS7 protocol) to another protocol (e.g., Transmission Control Protocol (TCP)/IP). The GW 204 can also include a Media GW (MGW) which functions similarly to existing TRCs used for implementing a GSM model. The MGW (not shown) includes a pool of Transcoder/Rate Adaptor (TRA) devices (not shown), which, when allocated, are connected to the A-interface. However, the IP network (e.g., GSM) side of the TRAs in the MGW are connected to respective UDP ports. Preferably, the GW 204 is connected to the IP network 208 via a separate router (not shown).
A third node connected to the IP network 208 is a Radio Network Server (RNS) 206. The RNS 206 functions similarly to a BSC used for implementing a GSM model. A primary difference between the RNS 206 and a BSC is that the RNS does not switch payloads and does not include a Group Switch (GS). As such, the RNS 206 preferably carries signalling only, and includes a pool of processors (e.g., the number of processors determined by capacity requirements). The RNS 206 provides a robust, general purpose distributed processing environment, which can be based on a standard operating system such as, for example, SUN/Solaris™. The 206 can serve one or more logical BSCs and is preferably connected to the IP network 208 via a separate router. As such, the payload can be routed directly between the GW 204 and RBS 202, without passing through the RNS′ 206 processors. The A-interface signalling is routed between the RNS 206 and GW 204.
The EDGE standard has been developed for a Time Division Multiple Access (TDMA) packet data system based on the GPRS technology. Essentially, the EDGE technology has been developed to provide an evolutionary path for GSM and TDMA operators to more effectively use the so-called 3rd Generation System's services, by building on the existing GPRS network infrastructure and radio air interface. EDGE technology is being developed to support best effort packet data transmissions at data rates of up to about 384 kbps, and Voice over Internet Protocol (VoIP) functionality.
In one approach being considered for an existing BSS, the PCU was to be located in the BSC (e.g., such as shown in FIG. 1). The reason for following this approach was because, at the time, it was the most effective way to introduce GPRS into the available BSS technology. As such, with the STM-connected RBSs in use at the time, which supported data rates of only 16 kb/s for each radio air timeslot, not many other options were available.
In another approach being considered for an IP-based BSS, the decision made was to locate the PCU in the RBS. The reasons set forth for this approach were as follows: higher transmission efficiencies could be attained, because the LLC frames could be treated as low priority packets in the transmission network; transmission network dimensioning could be accomplished easier than before, because peak allocations would not be needed, resulting in less transmission bandwidth needed; no synchronization protocol would be needed over the transmission network between the Radio Link Control/Medium Access Control (RLC/MAC) and CCU; lower signalling overhead would be needed; the lowest possible round-trip delay would occur, which would create no risk in stalling the RLC/MAC protocol used; there would be no risk in having to retransmit RLC/MAC blocks over the transmission network because of the ARQ approach used; and Moore's Law would make the manufacturing cost impact on the RBS much lower over time.
Subsequently, a number of drawbacks to the above-described approach for an IP-based BSS (to locate the PCU in the RBS) were recognized. First, the task of configuring the Network Service-Virtual Connection (NS-VC) on the Gb interface would have to be performed manually. As such, instead of having only one Gb interface to configure (as in the earlier approach), hundreds to thousands of Gb interfaces to the SGSN would have to be configured manually. This problem is especially significant since a primary objective of the IP-based BSS is to provide an effective plug-and play environment. Another drawback of the above-described approach is that a “Flush” function only works within one PCU. As such, when a Mobile Station (MS) performs a cell re-selection, the queue can be moved to the new RBS, but only within one PCU. With a PCU in the RBS, the queue would be discarded if the MS were to make a cell re-selection to a cell in another RBS with subsequent performance hits.
Another drawback of the above-described approach of locating the PCU in the RBS is that this approach hinders the development of a point-to-multipoint environment. In other words, one of the more important functions foreseen for an IP-based BSS is one that broadcasts information to groups of mobiles, so that it is beneficial to have a broad view of the BSS network. As such, the multi-point broadcast function should be centrally located, which is an impractical approach when the PCU is located in the RBS.
Still another drawback of the above-described approach is that it hinders the possibility of optimizing paging functions. In other words, the paging distribution function can be seen as being primarily a radio network function and not an SGSN function. If the approach was better able to take advantage of the knowledge about mobiles inside the Radio Access Network, the paging functions could be better optimized.
Notably, an important consideration for an IP-based BSS is that a GW device is needed for a number of reasons. For example, a GW can function as an anchor point for a handover. As such, in a system with real-time services (e.g., speech), such an anchor point is needed for handover at the ingress to the BSS. Next, a GW can function as the border of an administrative domain. Moreover, even if the Core Network in a system is also an IP network, a device such as a GW is needed as a delimiter for administrative purposes (e.g., assignment of IP addresses). Additionally, a GW can function for payload formatting and encryption conversions or terminations. As such, the payload formats and encryption methods can vary in Core Networks depending on the vendor. Also, a GW can enhance Quality of Service (QoS) mapping. For example, an IP-based BSS could be using Differentiated Services (Diff Serv) applications (e.g., as defined in IETF RFC 2475, “An Architecture for Differentiated Services”), and the Core Network could be using another type of service. Consequently, a GW could be used to map the QoS from one service to the other. Even if the Core Network also uses Diff Serv applications, the Core Network could also use another type of mapping of services to code points, for example. In other words, a GW provides the freedom for an operator to use different mappings.
Moreover, a GW can enhance the pricing of the bit-pipe from the SGSN. For example, one idea being considered for marketing GPRS is to price the peak rate for the pipe from the SGSN. This function would be extremely difficult to perform without a GW. Also, a GW would allow an operator to configure the links from the SGSN and MSC so as to keep the number of such links to a minimum. Finally, a GW could be provided for transcoding and signalling for backwards compatibility with the A- and Gb-interfaces.
For all of the above-described reasons, a new architecture for GPRS/EDGE applications in a BSS is needed (for GSM and TDMA systems). As described in detail below, the present invention provides such an architecture which successfully resolves the above-described problems and other related problems.